1. Field of the Invention
This invention relates to hand-operated chain blocks and, more particularly, to a hand-operated chain block which is light in weight and simple in construction with respect to its hand chain wheel portion and which permits safe and smooth hand chain operation.
2. Description of the Prior Art
Hitherto, various different types of hand chain wheel construction for hand operated chain blocks have been developed which are provided with measures for safe hand chain operation and which are reduced in weight and simplified in construction for the purpose of reduction in weight of the entire chain block.
In such situation, the present applicant has already proposed two types of chain block construction, namely, one disclosed in Japanese Utility Model Publication No. 19725/1973, and the other disclosed in Japanese Utility Model Publication No. 36204/1974.
The chain block disclosed in Japanese Utility Model Publication No. 19725/1973 comprises a positioning dowel formed on a hand chain guide plate, and a small slit formed in a hand chain wheel cover, the hand chain guide plate being adapted to be fixedly mounted to the chain block by a stay for hand chain wheel cover mounting and through engagement of the dowel with the small slit. The hand chain guide plate has a guide portion formed in such an overhanging pattern that it covers an upper edge portion of a side window of the hand wheel chain cover.
The other chain block disclosed in Japanese Utility Model Publication No. 36204/1974 has a hand chain cover of such split-type construction that it consists of an upper cover having a key-shaped section which covers a front upper peripheral portion of a hand chain wheel and a U-shaped lower cover which covers a front peripheral portion of the hand chain wheel other than covered by the upper cover. The lower cover is formed of a plate material having greater thickness than the upper cover and has at its opposite side ends a hand-chain guide plate integrally formed therewith. Opposite side ends of a front plate portion of the upper cover are placed in superposed relation with the corresponding ends of an upper portion of the lower cover, the superposed portions being secured by a common bolt to side plates of a chain block body, a median portion of the lower cover being secured by another bolt to the side plates.
However, these types of chain block construction are not fully satisfactory because of a number of deficiencies found therewith which are pointed out below; hence, further improvement has been demanded.
In the first mentioned disclosure, i.e., Japanese Utility Model Publication No. 19725/1973, the mounting arrangement for the hand chain guide plate is comparatively simple in itself, but the work required for engagement of the positioning dowel with the small slit in connection with the mounting of the guide plate is troublesome, which fact is disadvantageous from the standpoint of assembly work efficiency.
Another difficulty is that since the guide portion of the hand chain guide plate is located in an upper edge portion of the hand chain wheel cover, the entire side portions of the hand chain wheel are open and accordingly the hand chain is outwardly exposed, which fact is disadvantageous from the stand point of safety because the operator may possibly touch the hand chain wheel portion by hand at the open side portion, or because some falling object may possibly become engaged by the wheel portion.
In the second mentioned disclosure, i.e., Japanese Utility Model Publication No. 36204/1974, the guide plates for guiding the hand chain are small-sized plates provided at opposite ends of the lower cover and therefore the side portions of the hand chain wheel are substantially entirely open, which fact is disadvantageous from the standpoint of safety as is the case with the first mentioned disclosure.
Another drawback is that the lower cover for the hand chain wheel is comparatively thick walled, so that further reduction in weight is required of it, while on the other hand reduction in thickness for such purpose may possibly result in decreased strength of the lower cover.
Furthermore, both of the foregoing chain blocks have a deficiency in that in the case where the hand chain is pulled at comparatively high speed, if such operation is made in such condition that, for example, no load is being hung by a load chain, possible twists (snarls) cannot completely be straightened out by the hand chain guide plate. This means that the hand chain is wound in twisted condition around the hand chain wheel, smooth hand chain operation being thus prevented.